1. Field of the Invention
This invention relates to a disc clamping device, which is adapted to hold a disc clamper in a centered state even when the clamper is spaced apart from a turntable.
2. Description of the Prior Art
As a disc clamping device which is extensively used for a disc player for playing back a disc by rotating the disc in a state clamped between a turntable and a disc clamper, a following one is well known in the art.
The disc clamping device comprises a disc clamper having a boss for penetrating a center hole of a disc. The peripheral edge of the boss has a tapered surface for centering the disc. While the disc clamper is driven by a clamp support member for axial displacement toward a turntable, the tapered centering surface can cause horizontal displacement of the disc and thus center the disc with respect to the disc clamper.
As for the clamp support structure based on the clamp support member, the clamp support member has a circular hole, which is penetrated by a hung pin provided on the side of the disc clamper. The hung pin has a head greater in diameter than the circular hole, and the disc clamper is thus hung for vertical displacement relative to the clamp support member.
In this disc clamping device, when the disc clamper approaches and is brought into engagement with the turntable, the center of rotation of the turntable and the center of rotation of the clamper are brought to be coincident with each other. In order to permit the centering of the disc clamper by the turntable and also prevent the hung pin from touching the edge of the circular hole in the clamp support member when the disc clamper is rotated, a clearance is provided between the edge of the circular hole and the hung pin of the disc clamper by setting the outer diameter of the hung pin to be greater than the inner diameter of the circular hole.
The disc clamper is increased in size as a whole by increasing the stroke of displacement of the disc clamper. For the size reduction of the system, therefore, the displacement stroke of the disc clamper is desirably as small as possible.
As another aspect, by reducing the inclination angle of the tapered surface provided for the centering of the disc on the boss of the disc clamper, the horizontal component of force exerted to the disc when the tapered surface is engaged in the edge of the center hole of the disc is increased to obtain smoother centering of the disc with respect to the disc clamper. By reducing the inclination angle, however, the displacement stroke of the disc clamper that is necessary for horizontal displacement of the disc by a predetermined distance is increased, which is undesired for the size reduction of the system. Conversely, by increasing the inclination angle of the tapered surface for centering the disc, although the displacement stroke of the disc clamping device can be reduced, the horizontal component of force exerted to the disc when the tapered surface is engaged with the edge of the center hole of the disc is also reduced, which is undesired for the smooth centering of the disc with respect to the disc clamper.
As a further aspect, by increasing the clearance between the edge of the circular hole of the clamp support member and the hung pin of the disc clamper, the maximum eccentricity between the disc clamper and the disc is correspondingly increased. In order to permit smooth centering of the disc even with an increased eccentricity of the disc, it is necessary to increase the displacement stroke of the disc clamper or set an increased inclination angle of the tapered surface for centering the disc clamper. As noted above, however, increasing the displacement stroke of the disc clamper makes it difficult to reduce the size of the system, while setting an increased inclination angle of the tapered surface for centering the disc results in spoiling of the smooth centering of the disc. Conversely, reducing the clearance between the edge of the circular hole of the clamp support member and the hung pin of the disc clamper, leads to a problem that doing so makes it difficult to obtain the centering of the disc clamper by the turntable and smooth rotation of the disc clamper.
As a measure for solving the above problems, it is conceivable to let the disc clamper to be secured to the clamp support member by some means when the disc clamper is separated from the turntable.
As an example, Japanese Utility Model Publication No. 3-9162 shows a structure that the disc clamper is secured to the clamp support member by clamping the disc clamper with two levers when the disc clamper is separated from the turntable.
With this measure, the disc clamper is secured to the clamp support member independently of the clearance between the edge of the circular hole of the disc support member and the hung pin of the disc clamper even in the state of the disc clamper separated from the turntable. Thus, the maximum eccentricity between the disc clamper and the disc is not increased due to the clearance between the edge of the circular hole of the clamp support member and the hung pin of the disc clamper. That is, it is not necessary to increase the displacement stroke of the disc clamper with sacrifice of the system size reduction or set an increased inclination angle of the tapered surface for centering of the disc with sacrifice of the smoothness of centering the disc.
However, the structure shown in the Japanese Utility Model Publication No. 3-9162 requires the provision of the two levers for securing the disc clamper to the clamp support member. Besides, it is also necessary to provide a separate releasing mechanism for separating the levers from the disc clamper while the disc clamper approaches the turntable.
The invention was made for solving the above problems, and it has an object of attaining the size reduction and structure simplification, without spoiling the smoothness of centering the disc with respect to the disc clamper, of the disc clamping device, in which the hung pin provided at the center of the disc clamper and penetrating the circular hole of the clamp support member has the head greater in diameter than the circular hole to let the disc clamper be hung from and supported by the clamp support member, and also in which the clamp support member can cause the disc clamper to approach the turntable for clamping the disc between the turntable and the disc clamper while centering the disc with the tapered centering surface provided on the side of the disc clamper.
In the disc clamping device according to the invention, in which the hung pin provided at the center of the disc clamper and penetrating the circular hole of the clamp support member has the head greater in diameter than the circular hole to let the disc clamper be hung from and supported by the clamp support member, and also in which the clamp support member can cause the disc clamper to approach the turntable for clamping the disc between the turntable and the disc clamper while centering the disc with the tapered centering surface provided on the side of the disc clamper, at least either one of the portions of the edge of the circular hole and the head of the hung pin to be in engagement with each other, is formed as a tapered surface for centering the disc clamper, while the clamp support member is provided with an elastic member for pushing the head against the edge of the circular hole, thus permitting the disc clamper to be centered with respect to the clamp support member by the tapered centering surface in a state of the disc clamper separated from the turntable.
In this structure, since the disc clamper can be held secured to the clamp support member by the tapered centering surface for centering it even when it is in a state separated from the turntable, the maximum eccentricity between it and the disc is not increased due to the clearance between the edge of the circular hole of the clamp support member and the hung pin of the disc clamper. It is thus not necessary to set any particular large displacement stroke of the disc clamper, which is secured for the system size reduction. Also, it is not necessary to particularly increase the inclination angle of the tapered surface for centering the disc, and thus the smoothness of centering the disc is not spoiled. Furthermore, the disc clamper can be held secured to the clamp support member with a simple structure that at least either one of the portions of the head of the hung pin of the disc clamper and the edge of the circular hole of the clamp support member to be in engagement with each other is formed as a tapered surface for centering the disc clamper and that, the clamp support member is provided with an elastic member for pushing the head against the edge of the circular hole.
In a specific structure according to the invention, the tapered surface for centering the disc clamper is provided on the head of the hung pin provided on the center of the disc clamper, and the elastic member is provided on the clamp support member. The hung pin of the disc clamper penetrates the circular hole of the clamp support member, and the tapered surface for centering the disc clamper can be pushed against the edge of the circular hole by pushing the hung pin with the elastic member.
Thus, while the disc clamper is separated from the turntable, it is held by the clamp support member in a state that it is centered with respect thereto with the tapered surface for centering it, which is held pushed against the edge of the circular hole. When the disc clamper is caused by the clamp support member to approach the turntable for clamping the disc between the turntable and it, it is vertically displaced relative to the clamp support member, so that the tapered surface for centering it is separated from the edge of the circular hole.